Don't track frozendicts whose contents can never be tracked by the GC

When a frozendict is created, we can check whether all of its keys and values are objects that can never be tracked by the GC. If so, the frozendict can never be part of a reference cycle, so it can be left untracked, like gh-140232 did for frozenset. Since frozendicts are immutable, checking once at creation time is enough.

I'm preparing a PR for this.

Linked PRs

• gh-155178

先查看連結的 PR gh-155178，然後追蹤 frozendict 的建立及其垃圾回收器追蹤行為。完成標準是：鍵和值永遠不可能被 GC 追蹤的 frozendict 保持不被追蹤，而其他 frozendict 維持現有行為。